The present invention relates to a monitored, controlled door installation, such as the type employed in penal institutions and more specifically, to an improved door position monitoring arrangement.
Modern penal institutions of the medium to high security type employ sophisticated monitoring and control apparatus for cell doors. This is done to provide security for the guards, as well as the individual inmates, as it is necessary to control door operations so as to permit only one or possibly a few doors to be opened at any time. In one type of system, the doors are controlled electrically from a remotely located control panel. The correction officer will have a master key which can mechanically unlock any door in a group, with each inmate being issued an individual key capable of permitting the unlocking of his cell door from the exterior of the cell. Inside the cell, a push-button is provided which can operate the cell lock enabling the prisoner to exit the cell. The ability of the prisoner to operate the door from the interior of the cell is controlled by a main control panel, and as such each cell door lock can be rendered operable or inoperable at the election of the correction officer. Accordingly, when it is desired to control the number of inmates who have exited their cells at any one time it becomes extremely important that the control panel provide the correction officer with a correct indication as to the status of the various cell doors in the group under his control. To attain the desired monitoring of the status of the cell door, various types of apparatus are used, which are responsive to door position and capable of providing a control signal in relation thereto.
More specifically, the cell door lock mechanism generally includes a monitoring switch which is operated from a first door-open position to a second, door-closed position when the door is fully closed. When the door is open or ajar slightly, however, these switches and the lock mechanism are accessible and can be easily operated manually by an inmate to give a false signal that the door is closed and locked, when in fact it is not. To augment this type of lock monitoring arrangement it is a relatively common practice to employ a second door positioning monitor that cannot be easily circumvented by the inmate. The respective door positioning monitors are connected in series with a control panel so that a "door secure" signal is provided only when both monitoring units detect the closed position for the door. As such, ideally the second monitoring arrangement should be of a type that will give the "door secure" signal only when the door is approximately at the fully, and completely closed position. In this condition, the engagement of the door with the door stop and its alignment with the door jamb preclude the inmate from manually overriding the lock apparatus and the monitoring switch associated therewith.
One type of known secondary or supplemental monitoring arrangement employed in the art employs a switch which is associated with a hinge-type actuator, and is operated as a result of the pivotal movement of the door about the axis provided by the door hinges. The problem with this arrangement, however, is that the sensitivity of available switch designs is such that a certain minimum amount of movement of the operating arm for the switch is required before the switch is operated from one condition to another. Since the operational movement for the switch is produced as a result of the pivotal movement of the door, there exists with these prior art arrangements, a certain play or range of arcuate movement of the door that can take place when the door is moved from the closed to the partially opened or ajar position, before the switch is actuated. By way of example, assuming a two foot wide door, two degrees (2.degree.) of movement of the door will result in 11/16 inches of movement of the free edge of the door at the door jamb proximate the lock; correspondingly, three degrees (3.degree.) of movement will result in 11/4 inches of opening at the jamb. Openings of this size can be sufficient to enable an inmate to override the lock and the monitoring switch associated therewith so that the control panel may register a "door secure" condition when in fact a door is ajar and not secured.
The present invention provides an improved door positioning monitoring arrangement which attains increased sensitivity of operation through the arrangement and construction of the various elements of the overall assembly, while using conventional switch components. More specifically, with the prior art type of monitoring arrangements as discussed above, the ratio of door movement to movement available for operation of the monitoring switch was 1:1; that is, one degree (1.degree.) of door movement produced but one degree (1.degree.) of rotational movement about the hinge axis for transmittal to the switch actuating mechanism. As will be explained more fully hereinafter with regard to the drawings and the detailed description of the disclosed embodiment, with the present invention increased sensitivity is attained such that the ratio of movement available for switch operation to door movement is greater than 1:1. Basically, this result is attained by moving the operational pivot for the switch actuating mechanism away from the pivotal axis of the door as defined by the hinges, and by connecting the pivotally mounted door to said actuating mechanism by a control arm which is slidably connected to the door, yet will pivot relative to the switch actuating mechanism. With the present arrangement, it has been found that considerable improvement in the monitor sensitivity can be attained. As will be detailed more fully in conjunction with the detailed description of the illustrated embodiment, a ratio of actuator movement to door movement of 1.55:1 is easily attained. Thus, by way of example, with the prior art two degrees (2.degree.) of door travel will result in only two degrees (2.degree.) of rotational movement at the hinge axis, with the present invention, as illustrated, approximately three degrees--five minutes (3.degree.-5') of actuator movement is obtained.